Metal compositions



Unite States Patent METAL comrosmoNs Alan U. Seybolt, Scotia, N. Y., assignor to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Application December 7, 1948 Serial No..64,029

8 Claims. (Cl. 75122.7)

This invention relates to metal compositions and, more particularly, to novel uranium metal alloys.

Recent advances in nuclear physics have posed new problems with respect to the proper and completely satis-' factory utilization of certain radioactive materials. For example, early experiments with the use of uranium and its isotopes in neutronic reactors, neutron detecting apparatus and experimental piles presented evidence indicating that a new type of uranium alloy would be required in order .to successfully carry out a full experimental program. Many alloys were prepared but none of these successfully eliminated the deleterious effectson the alloys when they were subjected to high radiation densities at elevated temperatures in pile operation. Problems arose due to the fact that light elements such as lithium, boron, manganese, aluminum and cadmium have high absorption cross sections and are thus quite detrimental to a sustained fission reaction. It was felt, therefore, that a uranium alloy having a low absorption cross section and improved qualities of strength, hardness and machinability would add materially to the state of the art.

V Patented Feb. 3, 1959 as rhodium, palladium, or gold with about 98 atomic percent uranium have been found especially useful in imfully in the specific examples which follow.

Gold alloys containing a minor proportion by weight crease in hardness and yield strength, it should be pointed out that such alloys showed age hardening effects which may be deterimental in many applications. Furthermore, many of these alloys have an extremely high neutron absorption cross section and thus their utilityin these applications may be further limited.

It is, therefore, a primary object of this invention to prepare a strong, hard, yet machinable uranium alloy which is useful in neutronic reactors, neutron multiplying systems, and the like.

It is another object of this invention to prepare a machinable uranium alloy which can be heat treated to obtain a product with improved tensile and compression strengths and which is useful in neutronic reactors, neutron multiplying systems, and the like.

It is a further object of this invention to prepare a strong, hard, yet machinable uranium alloy comprising a major weight proportion of uranium.

It is another object of this invention to prepare an uranium alloy comprising a major Weight proportion of uranium, having the qualities of increased strength, machinability, and low neutron absorption cross section.

Still further objects of this invention will be apparent from the description and examples which follow.

The inventor, therefore, has developed novel radioactive metal alloys which add increased versatility to the use of these materials in many types of nuclear equipment. Alloys prepared by the method of this-invention comprise a major proportion of uranium and a minor proportion of at least one noble metal of the class of rhodium, palladium and gold. Alloys of between 1 and 3 atomic percent of a noble metal with the balance of uranium and preferably about 2 atomic percent of a noble metal, such An uranium alloy containing 2 atomic percent rhodium is prepared as in the following example.

Erample 1 158.6 grams of pure uranium metal in theform of broken lengths of uranium rod are placed in a beryllium oxide crucible. 1.4 grams of pure rhodium metal powder are placed in the refractory crucible which is then covered with a loose-fitting refractory lid. The charged crucible is placed in a vacuum furnace heated by induction and capable of being evacuated to about 0.2 micron of mercury. The furnace is evacuated to about 1 micron of mercury absolute pressure and the current is turned on. At a temperature of about Q C., the two metals melt and the alloy is formed. The melt is maintained at this temperature for 30 minutes to insure a completely homogeneous alloy, and at the end of this period the current is turned off, and the melt is permitted to cool. When the temperature has been reduced to about 250 C., the vacuum is broken and the solidified alloy is removed from the crucible. In the as-cast state the alloy has a bright, clean, well-consolidated appearance and has a Rockwell A hardness of about 63. By the treatment described hereinafter, the hardness may be increased to'about Rockwell A 72. g

Example II illustrates a method for the preparation .of an uranium alloy containing 2 atomic percent palladium. 1

Example II t 1.46 grams of pure palladium metal powder are mixed with 158.50 grams of uranium metal turnings and the mixture placed in a beryllium oxide crucible and covered with a loose-fitting lid of like material. The charged refractory crucible is placed in a high frequency induction furnace capable of being evacuated to 0.5 micron of mercury absolute pressure. The system is closed and the pressure is reduced to about 2 microns of mercury. Heat is applied by means of the high frequency induction circuit for a period of about 20 minutes which is sufiicient to raise the temperature to 1320 C. and to effect complete solution of the metals. The pressure is maintained at from 2 to 5 microns of mercury and heating is continued for an additional 20 minutes at which time the current is turned offand the melt permitted to cool and solidify. When the temperature has dropped to 300 C., the vacuum is broken and the alloy ingot is removed from the crucible. A thin oxide film may be present on the surface of the ingot but is easily removed by any polishing material and is not a serious detriment to most uses of the alloy. The alloy has a Rockwell A hardness of 66 in the as-cast state, which hardness may be increased to about 70 by the appropriate heat treatment.

Example III which follows gives the preferred embodiment of an uranium alloy containing 2 atomic percent gold.

Example III 1.66 grams of gold powder are weighed into a beryllium oxide crucible and 98.34 grams of uranium powder are added to the gold and thoroughly mixed. The crucible is covered with a refractory lid and the whole is placed carefully in a vacuum furnace which can be evacuated to 0.5 micron of mercury absolute pressure. Heat is applied, the pressure is reduced to about 1 micron mercury absolute pressure and the temperature is raised to 1250". C. At this temperature, melting of the metals occur and a solution of two metals is obtained.

The temperature is held between 1250 C. and 1350 C, for aperiod of l hour At the end of this time, the alloy is completely homogeneous and is permitted to cool by thermal convection until a solid solution isobtained. The vacuum is broken and the resulting alloy removed from the crucible. The alloy has a bright, clean appearance and a Rockwell A hardness of about 63. By the proper heat treatment this value may be increased to about Rockwell A 70.

The alloys described hereinbefore are useful in improving the mechanical properties of uranium and have the further advantage that the noble alloying metal has, for practical purposes, no adverse effects on the nuclear properties of the radioactive material. Uranium alloys containing the noble metals herein described have the advantage that cracking isreduced to a negligible amount in the as-cast state. Hardness of the as-cast rhodiumuranium .and gold-uranium alloys have been determined to. be Rockwell A 63, and for the palladium-uranium alloy, Rockwell A 66, whereas normal uranium has an as-cast hardness of about Rockwell A 50. These alloys are dense, yet are readily machinable, and may be subjected to heat treatment which further increases their desirable properties. For example, when a gold-uranium alloy is heat treated by soaking for five hours at 900 C. and water quenched, then reheated for two hours at 400 C. and aged for 48 hours, the hardness is found to be about Rockwell A 70. Rhodium-uranium and palladiumuranium alloys respond equally well to such treatment. The hardness of a rhodium-uranium alloy is increased to a value of about Rockwell A 72, and the hardness of the palladium-uranium alloy is increased to a value of about 70 on the same scale. Additional heat treatment of the kind just described does not aifect the hardness materially. Normal uranium similarly treated has a hardness of Rockwell A 56.

While the foregoing examples have disclosed the preferred proportions of the alloying metals, it is to be understood that other proportions may be successfully employed. For example, satisfactory alloys can be prepared containing from 0.1 to 5.0 weight percent of the noble metal with the balance uranium.

Although the examples have been directed to normal uranium it is possible to use individual isotopes of uranium, such as uranium 238, uranium 235, uranium 233, or various mixtures thereof with equally beneficial results.

It is thus seen that this invention discloses new and novel alloys that may readily be obtained by methods and equipment which are assembled in well-equipped metallurgical laboratories and that have many desirable properties not found in alloys prepared by methods known before.

As many widely difierent embodiments of the invention can be made without departing from the spirit and scope thereof, it is to be understood that this application is not to be limited except as indicated in the appended claims.

What is claimed is:

i. A novel alloy consisting of from 0.1 to 5.0 weight percent of: at least one noble metal of the class consisting of rhodium, palladium and gold, and the balance of uranium.

2. A novel alloy consisting of from 1' to 3 atomic percent of at least one noble metal of the class consisting of rhodium, palladium and gold, and the balance of uranium.

3. A novel uranium alloy which consists of from 1 to 3 atomic percent of rhodium and the balance of uranium.

4. A novel uranium alloy which consists of from 1 to 3 atomic percent of palladium and the balance of uranium.

5. A novel uranium alloy which consists of from 1 to 3 atomic percent of gold and the balance of uranium.

6. A novel'uranium alloy consisting of uranium and rhodium, the latter element being present in the amount of 2 atomic percent.

7. A novel uranium alloy consisting of uranium and palladium, the latter element being present in the amount of 2 atomic percent.

8. A novel uranium alloy consisting of uranium and gold, the latter element being present in the amount of 2 atomic percent.

References Cited in the file of this patent UNITED STATES PATENTS 

2. A NOVEL ALLOY CONSISTING OF FROM 1 TO 3 ATOMIC PERCENT OF AT LEAST ONE NOBLE METAL OF THE CLASS CONSISTING OF RHODIUM, PALLADIUM AND GOLD, AND THE BALANCE OF URANIUM.
 3. A NOVEL URANIUM ALLOY WHICH CONSISTS OF FROM 1 TO 3 STOMIC PERCENT OF RHODIUM AND THE BALANCE OF ARANIUM. 